Motors exist in the prior art in a variety of forms. Some are operated by fluid power (i.e., those of the expansible chamber type), while others are operated electromagnetically. In many of these, one part (i.e., the rotor) rotates relative to a stationary part (i.e., the stator). Often, the rotor is associated with a shaft.
When such motors are incorporated into larger systems, it may be desired to monitor the angular position of the rotor relative to the stator. For example, in a stepping motor servosystem, the desired angular position of the rotor relative to the stator may be provided as an electrical command. The actual relative position between the rotor and stator may be determined by a transducer, such as a resolver or the like, and the output thereof provided as a negative feedback signal. The command and feedback signals are algebraically summed so as to drive the error therebetween toward zero.
A revolver itself typically has a shaft rotatably mounted on a body. The resolver body is typically mounted on the motor housing, such that the resolver shaft is coaxial with, and coupled to, the motor shaft. In mounting such a device on a motor housing, the body must initially be angularly adjustable relative to the motor housing in order to allow nulling of the transducer. Once the initial relative angular position between the transducer body and motor housing has established, the transducer body must be thereafter restrained against unintended axial and rotative movement relative to the motor housing. At the same time, the mounting mechanism should be adjustable to allow for subsequent adjustment and modification of such relative angular positions.
Such position transducers are commonly available off-the-shelf in a form which an angular groove extends radially into the transducer body from a cylindrical outer surface, adjacent one end face. Another standard style has one or more annular flanges extending radially outwardly from the cylindrical side wall. In either case, such configuration provides a groove, either raised or recessed, on the body. This groove is, on information and belief, deliberately provided to receive and accommodate a plurality of "synchro clamps", by which the transducer may be mounted on the housing. Thus, such clamps have typically been provided so as to engage both the transducer body and the housing to adjustively mount the transducer body thereto. Various types and configurations of such clamps are arrayed and described in Fischer, "A Shopper's Guide to Synchro Clamps", Machine Design (Jan. 27, 1972)(at pp. 104-107), and in U.S. Pat. No. 2,896,295.
These synchro clamps are intended to provide a low-cost means for mounting the transducer on the motor housing. However, it is Applicant's belief that such clamps as have been developed heretofore have inadequately restrained the transducer body against rotation relative to the motor housing. In fact, it has been Applicant's experience that with such prior art synchro clamps, the transducer body may actually rotate unintentionally during use relative to the housing by extemely small increments. However, depending upon the end use to which the motor is put, even such small incremental angular displacements may aggregate over a long duty cycle (e.g., 50,000 cycles). Hence, the individual error may aggregate and accumulate to provide a significant relative angular position error, with the concomitant effect that null shift in the transducer output signal occurs.
Upon information and belief, many of these prior art synchro clamps were designed and intended to exert principally an axial force on the resolver body. Some clamps were designed to provide both axial and radial forces on the transducer body. However, this was done at the expense of actually bending the shank of a screw, which was used to tighten the clamp against the body and housing. (See, e.g., FIG. 2 of said Machine Design article, at p. 107, and accompanying text at p. 106). Indeed, in this arrangement, the clamp geometry was such that only a fraction of the force exerted by the screw on the clamp was transmitted to the transducer body. Moreover, because this implementation acutally contemplated that the shank be bent as the screw was tightened, the operator was hesitant to adequately tighten the screw for fear of breaking it. Moreover, it is now believed that the inability of such prior art synchro clamps to exert an adequate radial force on the transducer body, was responsible for permitting such undesired relative angular movement between the clamped body and housing.
An improved transducer clamp should have the following characteristics or properties: (1) the mounting screw should not be bent, in order that it may be tightened as much as possible, (2) the clamp should offer the capability of holding the transducer body at any selected angular position relative to the housing, both initially and after some use, (3) the clamp should be usable with standard off-the-shelf transducer configurations, (4) the clamp should exert a significant radial load on the transducer body to prevent unintended relative angular rotation during use, (5) the clamp should not impart rotation to the transducer while tightening the fastener, and (6) such a clamp should be economical to both make and use.